1. Field of the Invention
The present invention relates to a vehicular navigation apparatus that performs route guidance along a route found and set between a current position and a destination or an intermediate point.
2. Description of the Related Art
Vehicular navigation apparatuses are designed to search for a route from a current position to a destination or the like on the basis of an inputted location such as a destination or the like, and perform route guidance based on the route found by the search, thereby reducing the difficulties that a driver faces when driving on roads unfamiliar to the driver. For this end, a typical vehicular navigation apparatus has a function for searching for a route from a current position to a destination upon input of the destination, and functions to display a guiding route found by the search and the current position of the vehicle. With these functions, the vehicular navigation apparatus detects the current vehicle position, and displays the current vehicle position on a the route found by search, in order to provide route guidance.
While being guided along a route found by the search, a driver may deviate from the route for some reason, for example, the driver's misperception of a target object or a misunderstanding. To cope with such a deviation from the route, Japanese patent laid-open application No. SHO 61-38518, for example, proposes a vehicular navigation apparatus which determines that a vehicle has deviated from the set route if the current position of the vehicle is apart from the route by a predetermined distance or greater, and then performs a search again to find a route from an intersection located ahead of the vehicle current position to the destination.
Considering the time required to re-find a guiding route from the current position to the destination after detection of a deviation from route, however, it is possible that the above-described type of apparatus, that searches for a route from an intersection ahead of the vehicle, may find such a new route only after the vehicle has passed the intersection. If this should happen, the driver will have passed the intersection without knowing the direction which should have been taken at the intersection in accordance with the search results. Therefore, the driver may well go in a direction different from the direction indicated by the search results. In addition, the search results will not take into account the direction in which the vehicle is traveling after passing the intersection in the above-described manner. Thus, in such an event, the driver will likely go straight through the intersection, even if the driver should have turned there, for example, to the left, according to the new route to the destination determined by the search, and will learn of the search results only after passing the intersection.
Problems similar to those mentioned above may occur when the apparatus searches for a route to return to the previously set route after detecting deviation from that route. Since the time required to find a route from the currently detected position to the destination or back to the previously set route after detection of deviation therefrom is significant, it can happen that an optimal route connecting to an intersection is displayed only after the vehicle has traveled through that intersection in a direction different from the direction according to the optimal route. Thus, the starting point of a route displayed as a result of the search will not necessarily be ahead of the vehicle. Furthermore, even if a route is displayed such that a crucial point, for example, for turning right or left, is ahead of the vehicle, the vehicle may be coming so close to the point that the driver cannot react in sufficient time to execute the guidance instructions.
As for the above-described route re-search methods, the present applicant has proposed a search method that searches for a correcting route to return to the previously set route and connects the connecting route to the previously set route and a search method wherein the search may develop an entirely new route to the destination or an intermediate point (Japanese patent application laid-open No. HEI 6-68389). The present applicant has also proposed a route search method that searches for another guiding route based on the route set beforehand (Japanese patent application No. HEI 6-228174). However, these methods are not free from the above-mentioned problems. In addition, similar problems will obviously arise with an initial route search performed upon the initial input of a destination or an intermediate point if a vehicle has started to travel before the result of search is output in response to the route search instruction. In such a case, the vehicle will be traveling on a road off the set route by the time when the search results are output.